The visit by Kim Sook comes three days after a US envoy returned from Pyongyang with some 18,000 pages of documents on the history of a plutonium bomb-making programme dating back to 1986.

A review of these records "will be an important first step" in verifying that North Korea's eventual nuclear declaration is complete, the US State Department has said.

Kim will meet his Chinese counterpart Wu Dawei to discuss pending issues concerning the six-party talks aimed at ending North Korea's nuclear programmes, said foreign ministry spokesman Moon Tae-Young.

South Korean officials have said they hope the next round of six-nation negotiations can be held late this month or in early June, after the North submits its declaration to talks host China.

In return for an acceptable declaration, the United States has promised to to ease some of its sanctions against the hardline communist state.

The North, which staged its first nuclear test in October 2006, is disabling its reactor and other plants at Yongbyon under a deal reached last year with the United States, China, Japan, Russia and South Korea.

But disputes over the declaration due last December 31 have blocked the start of the final phase of the process -- the permanent dismantling of the plants and the handover of all material.

The declaration is crucial to verifying that all material, including stockpiled plutonium which could be used for bomb-making, is accounted for.

In return for total denuclearisation, the North would receive energy aid, a lifting of US sanctions, the establishment of diplomatic relations with Washington and a formal peace treaty.

The US had said the declaration must also clear up suspicions about alleged secret uranium enrichment and about suspected proliferation to Syria.

The North denies both activities. Under a reported deal, it will merely "acknowledge" US concerns about the two issues in a confidential separate document to Washington while making its formal declaration to China.

Kim Byung-Kook, senior presidential secretary for foreign affairs and security, will travel to Beijing on Wednesday for talks focusing on President Lee Myung-Bak's upcoming visit to China.

The two Kims will stay until Friday for talks with Chinese officials including Vice Foreign Minister Wang Yi, the ministry spokesman said.

Lee will visit China from May 27-30 for talks with President Hu Jintao and other leaders focusing on bilateral relations and efforts to resolve the North Korean nuclear issue, the presidential Blue House said.

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